Well service pumps are employed for pumping fluids into wells for treatment, such as hydraulic fracturing. The flow rates and the pressures are often high; pressures may exceed 10,000 psi. A typical well service pump has a power end that connects to a separate fluid end block with stay rods. The power end reciprocates plungers that stroke within plunger bores in the fluid end block. A packing gland member is used to seal the interface between the plunger and the fluid end block.
Packing gland members come in a range of standard sizes and are used for different plunger diameters with the same fluid end block. The packing gland member is bolted to the fluid end block. However, a bolt-on packing gland requires a seal that can create problems. Also, the bolt-on arrangement may create higher stresses in certain areas, leading to stress fractures. Often, the packing gland is held to the power end via tie rods. This too can lead to higher stresses in certain areas.